Study On Steering Performance Of Independent-drive Vehicle With Multi-axle

With the development of electric drive technology,the independent drive multi axle vehicle has gradually become an important type of today’s military wheeled vehicle.The application of military vehicles is complex and changeable,which needs good maneuverability and handling stability.As independent drive of multi axle vehicle,the driving force of each wheel is controllable independently,so there are more ways in vehicle dynamics control to improve the steering performance.Due to the complexity of its structure,the accuracy,rationality and effectiveness of the control system are also put forward higher requirements.Therefore,it is necessary to carry out in-depth research and analysis for the independently drive multi-axle vehicle steering control system.In this paper,8×8 independent drive multi-axle vehicle is taken as the research object.Based on the vehicle dynamics,the optimal control of the steering performance is studied,and the target of the optimal steering control under different input and vehicle movement conditions is determined,the control strategy of driving stability,low-speed mobility and high speed handling stability is studied,through the mathematical model simulation,state observer-based co-simulation and real vehicle test,the control system was analyzed and verified,a complete package is provided about steering performance optimization control of independent drive vehicles.Based on the vehicle dynamics,an 11-DOF vehicle system model of 8×8 independent drive multi-axle vehicle is established,including the longitudinal,lateral and yaw movement of the vehicle body and the turning movement of 8 wheels.The model includes the entire vehicle model,the driving system model and the driver model,and the load transfer and tire non-linear characteristics are taken into account.a "human-vehicle" system is established to conduct a more comprehensive study on the steering performance of the vehicle;meanwhile,a linear 2-DOF model is established as the reference of the vehicle motion state;and the simulation and verification according to the parameters of the test sample vehicle,which proves the accuracy and rationality of the model and can be used as the basis for the subsequent research on steering performance optimization control.Based on the analysis of the limits of vehicle’s steering and side slip,the vehicle’s motion state is determined.The control objectives of driving stability,low-speed mobility and high speed handling stability are determined.According to the different characteristics of vehicle movement state under different sub-targets,the vehicle reference state is identified and amended,and the corresponding control strategies are researched:(1)For driving stability,the related factors that affect the driving stability of the vehicle are analyzed and the control variables are established.Considering that the vehicle always runs in this linear movement state,a simple and fast control system with high reliability is designed.The PID control algorithm is applied to improve the driving stability of the vehicle by increasing or decreasing the wheel driving force on both sides respectively.(2)For high-speed handling stability,considering that the vehicle is in the limit motion state and the simple change of the wheel drive force can not achieve a good control effect.,in order to more accurate,the method of stratified control is adopted to solve the calculation of the yaw moment and the rational distribution of the driving torque,the upper controller based on sliding mode control algorithm to calculate the amount of vehicle yaw moment,.controllers are designed for yaw rate and centroid slip angle and the selection logic is determined.The lower layer controller assigns the driving torque reasonably through the yaw moment.For the constrained optimization problem,based on the optimal control theory,the adjustment amount of the driving torque is distributed on different wheels,and the optimal objective function is added on the basis of determining the error objective function so that the allocation result can improve the vehicle handling stability while also ensuring the adjustable tire force margin.(3)For low speed mobility,the entry conditions of vehicle maneuverability control are determined through the analysis of the driver’s control input and the vehicle movement state.The maneuverability of the vehicle is simulated under different driving force variation.Considering that the driver’s need of improving vehicle maneuverability and driving adaptability to the vehicle,an open-loop control strategy for vehicle maneuver control is developed.The simulation test is used to analyze the rationality and effectiveness of the control strategy.The joint simulation is analyzed in order to further study the effectiveness of the control system.First of all,according to the practical application status of the vehicle,a vehicle state observer is designed based on the unscented Kalman filter algorithm for vehicle status information and road surface parameter information which is not easy to measure at present.The observer can obtain the longitudinal velocity,lateral velocity,centroid slip angle,the dynamic parameters of the tire and the road surface adhesion coefficient.And a joint simulation test platform based on Trucksim and Simulink is established.Under different operating conditions,a comprehensive simulation analysis of the vehicle steering performance optimization control system proposed in this paper is carried out,which proves the effectiveness and rationality of the control system.Finally,a 8×8 independent drive multi-axle vehicle real vehicle test platform is established and a real vehicle test study is carried out to verify and analyze the real-time reliability of the control system.The vehicle driving stability test and low-speed mobility test were carried out.The real-time control effect was analyzed by different working conditions.The experimental results show that the control strategy proposed in this paper can control the vehicle in real time according to the driver’s input and the state of the vehicle,which improves the steering performance of the vehicle.